This invention relates to data processing technology, and more particularly to technology which is especially effective when applied to a microprocessor.
A microcomputer system is constructed of a microprocessor, storage devices such as a ROM (read-only memory) and a RAM (random access memory), an input/output interface (I/O), etc. In this case, the use of a dynamic RAM is better than the use of a static RAM because of the merit that the system can be arranged less expensively.
Since, however, the dynamic RAM adopt an address multiplexing system and requires a refresh operation, the control thereof is more troublesome than those of the ROM and the static RAM. Therefore, any of prior-art microprocessors has been constructed so as to be capable of direct access to the ROM and the static RAM. When arranging the system to use a dynamic RAM, it has been necessary to dispose complicated external circuits including circuits for forming RAS (row address strobe) signal, CAS (column address strobe) signal and a signal RFSH, which indicates a refresh timing, which are required for operating the dynamic RAM on the basis of clock signals or control signals delivered from the microprocessor (refer to `Microcomputer` published by CQ Shuppan Kabushiki-Kaisha, No. 6, 1982, pp. 87-89).
In this manner, the use of the dynamic RAM for the prior-art microprocessor has eed to the problems that the design of the system becomes difficult and that the packaging area of the system becomes large.
A certain prior-art microprocessor has a built-in refresh counter which generates the refresh address of the dynamic RAM. Even with such a microprocessor, the RAS signal and the CAS signal must be produced by the external circuits.